The constantly increasing demand for synthetic quartz crystals by the communications, telephony, electric watch, and frequency and time standard industries, has pushed commercial sources beyond present capacities, both with respect to quantity and quality of crystal supply. Most of the synthetic material currently supplying this demand consists of crystals grown from natural crystalline quartz nutrient handpicked for quality but of limited purity level.
Considering the existence of vast supplies of amorphous silica on this continent, it would be advantageous if such a material could be used to grow synthetic crystals. Very high purity fused silica is now being produced from these sources and is now readily available. Past efforts to grow high quality quartz crystals from amorphous nutrient have not been too successful: poor quality crystals have been obtained that are off-color and near opaque, as well as physically criss-crossed with multiple fractures. Buehler, in U.S. Pat. 2,785,058, briefly discussed some of these efforts in his review of the art. Walker, also, reports on the ineffectiveness of the constant temperature hydrothermal method for growing quartz crystals from amorphous silica, and solves the problem by resorting to a temperature difference method using a crystalline quartz nutrient. ("Hydrothermal Synthesis of Quartz Crystals.") Sawyer (3,101,259) similarly grows crystals from an aqueous sodium carbonate solution of a siliceous material such as pure natural quartz crystals in an autoclave in which there is maintained a temperature difference ranging from 4.degree. to 19.degree. C. between the lower mineral-dissolving chamber, typically at about 356.degree. C., and the upper crystal-growing chamber, typically at about 339.degree. C.
Among the methods of obtaining quartz crystals from amorphous silica that have been alluded to earlier, that of Brogue et al. (2,680,677) involves the disposition of .alpha.-quartz on .alpha.-quartz seed crystals at temperatures within the range of 500.degree.-550.degree. C. at a pressure of 1200 psig. A thirty-fold weight increase of the seed is disclosed. More recently, Hoover (2,965,448) discloses a process for converting amorphous silica into a form of crystalline quartz, using a temperature range of 450.degree. to 700.degree. C. at a pressure of 1500 to 3200 atmospheres for a period of about 10 hours. Hoover, however, is not concerned with single crystal growth.
Other patents of interest in the quartz crystal growing field include: Kohman (2,895,812) which discloses the use of a baffle between the solution zone and the crystallization zone of the quartz-growing autoclave, and Chardonnet (2,914,389), Turobinsici (2,931,712), and Jafee et al. (2,923,605), who disclose various seed configurations and arrangements.